Attempts at making vaccines against HIV-1 have met with limited success, as measured by the criterion of achieving in animals an immune response similar or equivalent to that of humans that are sero positive to HIV-1. The major goal, not previously attained, has been the generation of antibodies that are virus neutralizing in vitro at titers reaching both the level and complexity (i.e., ability to neutralize more than one isolate) seen in human sera from infected individuals. All of the neutralizing antibodies in humans have mapped to the envelope protein, gp160, or one of its component parts (gp120 or gp41), and thus most vaccine efforts have concentrated on the development of envelope-protein-related antigens.
Five types of such antigens have been developed: (1) purified gp120 derived from HIV-infected tissue culture cells (referred herein as "viral-derived gp120"); (2) gp120 made in cells infected with recombinant viruses, such as vaccinia or baculovirus ("live-virus-vector-derived gp120 and gp160"); (3) recombinant gp120 made in mammalian cells ("recombinant mammalian gp120," sometimes referred to incorrectly as recombinant native gp120); (4) recombinant denatured polypeptides that represent all or various portions of gp120 and gp41 ("recombinant denatured antigens"); and (5) peptides that represent small segments of gp120 and gp41 ("peptides").
Immunogenicity experiments have been completed with all of these types of antigens, with fairly uniform results. In general, the antigens are highly immunogenic as adjuvanted in a variety of species. They have generated antibodies capable of neutralizing the homologous isolate of HIV-1, but they poorly or not at all neutralize non-homologous isolates. The levels of neutralization also have not (in general) reached the level of neutralizing titer found in infected humans.
For example, fully glycosylated gp120 natural purified from virus or produced by genetically engineered mammalian cells, non-glycosylated gp120 produced in yeast, and a fragment of gp120 produced in E. coli can all elicit HIV-1 neutralizing antibodies in experimental animals. For the most part, the responses of animals immunized with virion or recombinant gp120 antigens are effective in neutralizing only the virus isolate from which the gp120 antigen originated. One exception is the work of Berman et al. (reference 1 below) showing that purified recombinant HIV-1 gp120 secreted by genetically engineered Chinese hamster ovary cells elicited group-specific neutralizing antibodies in chimpanzees.
Another factor that has been particularly difficult to overcome when preparing HIV-1 vaccines is sequence diversity. HIV-1 and HIV-2 are characterized by having a very high level of sequence diversity that is most pronounced in the gp120 portion of the envelope. This sequence diversity is clustered in regions known as hypervariable regions. Many groups have proposed using a vaccine cocktail, comprising antigenic substances derived from a variety of HIV isolates, to provide protection against a broad range of infective sources.
Accordingly, there remains a need for an antigenic substance having immunological and other protein/protein binding properties of gp120 as it is presented on an HIV-1 virus particle. In particular, antigenic substances capable of inducing neutralizing antibodies, preferably using a single source material that induces neutralizing antibodies against a variety of field isolates, are highly desirable.
Relevant Literature
The following publications are all directed to the five types of vaccine candidates described above:
(1) Berman et al., "Human Immunodeficiency Virus Type I Challenge of Chimpanzees Immunized with Recombinant Envelope Glycoprotein gp120," Proc. Natl. Acad. Sci. USA (1988) 85: 5200-5204;
(2) Berman et al., "Expression and Immunogenicity of the Extracellular Domain of the Human Immunodeficiency Virus Type I Envelope Glycoprotein, gp160," Journal of Virology (1989) 63: 3489-3498;
(3) Nara et al., "Purified Envelope Glycoproteins from Human Immunodeficiency Virus Type I Variance Induced Individual, Type-Specific Neutralizing Antibodies," Journal of Virology (1988) 62: 2622-2628;
(4) Arthur et al., "Serological Responses in Chimpanzees Inoculated with Human Immunodeficiency Virus Glycoprotein (gp120) Subunit Vaccine," Proc. Natl. Acad. Sci. USA (1987) 84: 8583-8587;
(5) Evans et al., "An Engineered Polio Virus Chimaera Elicits Broadly Reactive HIV-1 Neutralizing Antibodies," Nature (1989) 339: 385-388;
(6) Barrett et al., "Large-Scale Production and Purification of a Vaccinia Recombinant-Derived HIV-1 gp160 and Analysis of its Immunogenicity," AIDS Research and Human Retroviruses (1989) 5: 159-171;
(7) Earl et al., "Isolate--and Group-Specific Immune Response to the Envelope Protein of Human Immunodeficiency Virus Induced by a Live Recombinant Vaccinia Virus in Macaques," AIDS Research and Human Retroviruses (1989) 5: 23-32;
(8) Putney et al., "HTLV-III/LAV-Neutralizing Antibodies to an E. coli--produced Fragment of the Virus Envelope," Science (1986) 234: 1392-1395;
(9) Steimer et al., "Genetically Engineered Human Immunodeficiency Envelope Glycoprotein gp120 Produced in Yeast is the Target of Neutralizing Antibodies," Vaccines 87 (1987) 236-241;
(10) Steimer et al., "Recombinant env and gag Polypeptides in Characterizing HIV-1-Neutralizing Antibodies," Vaccines 88 (1988) 347-355;
(11) Ho et al., "Human Immunodeficiency Virus Neutralizing Antibodies Recognize Several Conserved Domains on the Envelope Glycoproteins," Journal of Virology (1987) 61: 2024-2028; and
(12) Palker et al., "Type-Specific Neutralization of the Human Immunodeficiency Virus with Antibodies to env-Encoded Synthetic Peptides," Proc. Natl. Acad. Sci. USA (1988) 85: 1932-1936.